\(\frac{37-x}{x+13}=\frac{3}{7}\)
\(\Leftrightarrow3.\left(x+13\right)=7.\left(37-x\right)\)
\(\Leftrightarrow3.x+13.3=7.37-7.x\)
\(\Leftrightarrow3x+39=-7x+259\)
\(\Leftrightarrow3x+7x=259-39\)
\(\Leftrightarrow10x=220\)
\(\Leftrightarrow x=22\)
37−xx+13=3737−xx+13=37
⇔3.(x+13)=7.(37−x)⇔3.(x+13)=7.(37−x)
⇔3.x+13.3=7.37−7.x⇔3.x+13.3=7.37−7.x
⇔3x+39=−7x+259⇔3x+39=−7x+259
⇔3x+7x=259−39⇔3x+7x=259−39
⇔10x=220⇔10x=220
⇔x=22